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## Homework Statement

A hollow sphere of radius [itex]r_1[/itex] is placed at the centre of a larger hollow sphere of radius [itex]r_2[/itex].

Both spheres have a uniformly distributed total charge of +q

Find the preassure [itex]p(r_2 , q)[/itex] which acts on the outer sphere.

## Homework Equations

[itex]\oint\textbf{E.n}dS = 4\pi k Q[/itex]

[itex]p = \frac{dF}{dA}[/itex]

## The Attempt at a Solution

Inside the larger sphere, there is no contribution to electric field from the large sphere, so just consider the electric field at [itex]r_2[/itex] due to the inner sphere:

[itex]E(4\pi r_2^2) = 4\pi k q[/itex]

[itex]E = \frac{kq}{r_2^2}[/itex]

since [itex]F = qE[/itex]

the force acting at [itex]r_2[/itex]:

[itex]F(r_2) = \frac{kq^2}{r_2^2}[/itex]

[itex]p = \frac{F}{A}[/itex]

[itex]p = \frac{kq^2}{4\pi r_2^4}[/itex]

does this look right?

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